#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<vector>
#include<string>
using namespace std;
class Solution {
public:
    int numDecodings(string s) {
        int n = s.size();
        vector<int> dp(n + 1);
        dp[0] = 1;
        dp[1] = s[1 - 1] != '0';
        for (int i = 2; i <= n; i++)
        {
            if (s[i - 1] != '0')
                dp[i] += dp[i - 1];
            int b = (s[i - 2] - '0') * 10 + s[i - 1] - '0';
            if (b >= 10 && b <= 26)
                dp[i] += dp[i - 2];
        }
        return dp[n];

    }
};